<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>倒计时</title>
	</head>
	<body>
		 <script type="text/javascript">
		        window.onload = function(){
		            var i = 900;
		            var timer = setInterval(function(){
		                if(i== -1){
		                    clearInterval(timer);
		                }else{
		                    document.body.innerHTML = i;
		                    --i;
		                }
		            },1000);
		        }
		    </script>
	</body>
</html>
